Ink jet printing processes are essentially of two types, continuous stream and drop-on-demand.
In continuous stream ink jet printing systems, ink is emitted in a continuous stream under pressure through a nozzle. The stream breaks up into droplets at a fixed distance from the nozzle. If a specific location on the recording sheet has to be printed the individual droplets are directed to this specific location, otherwise they are directed to a gutter. This is done for example by charging unnecessary droplets in accordance with digital data signals and passing them through an electric static field which adjusts the trajectory of these droplets in order to direct them to the gutter. The inverse procedure may also be used wherein uncharged droplets are directed to the gutter.
In the non-continuous process, or the so called "drop-on-demand" systems, a droplet is generated only in accordance with digital data signals if it is to be placed onto the recording sheet.
The most important part of an ink for ink jet printing are the dyes. Although a number of dyes have been proposed none meets all the necessary requirements.
Yellow monoazo dyes or mixtures of such dyes and their use in inks for ink jet printing are described for example in U.S. Pat. No. 5,684,140 or in patent applications WO 98-12263, EP 0,567,036 and EP 0,755,984.
The monoazo dye of formula (1) ##STR2##
is described in patent application EP 0,755,984 (example 104).
The monoazo dye of formula (2) ##STR3##
is described in patent application WO 98-12263 (example 19).
The two monoazo dyes mentioned above as well as other structurally similar dyes mentioned in this patent and in these patent applications, representing the state of the art, however do not satisfy all the required demands when used in recording liquids for ink jet printing. Neither do they satisfy all the required demands if they are used in the formulation of inks for ink jet printing that should provide brilliant images or colorings with excellent color rendition (extended gamut) on any type of recording medium as plain or coated paper, coated or uncoated, opaque or transparent synthetic materials, because these yellow monoazo dyes are either not brilliant enough or too reddish.
Dyes used for recording liquids for ink jet printing have to show a good solubility in the essentially aqueous ink liquid, they have to penetrate into the recording medium and should not show dye aggregation on the surface of the recording medium ("bronzing"). They need to provide printed images having high optical density, good water fastness and good light stability. They need to be stable in the ink even when the recording liquid is stored for a long time under adverse conditions.
Various types of compositions have been proposed as inks for ink jet printing. Typical inks comprise one or more dyes, water, organic cosolvents and other additives.
The inks have to meet the following criteria:
(1) The ink gives high quality images on any type of recording medium. PA1 (2) The ink gives printed images exhibiting good water fastness. PA1 (3) The ink gives printed images exhibiting good light stability. PA1 (4) The ink gives printed images exhibiting excellent smudge behavior. PA1 (5) The ink does not clog jetting nozzles even when these are kept uncapped while recording is suspended for long periods. PA1 (6) The ink can be stored for long periods of time without deterioration of its quality. PA1 (7) The values of the physical properties of the inks as viscosity, conductivity and surface tension are all within defined ranges well suited for the intended use. PA1 (8) The ink has to be non toxic, not flammable and safe. PA1 R.sub.1 represents hydrogen or alkyl with 1 to 6 C atoms; PA1 n is 2, 3 or 4; PA1 A represents NR.sub.3 R.sub.4, wherein R.sub.3 and R.sub.4 independently represent hydrogen; alkyl with 1 to 8 C atoms; substituted alkyl with 2 to 6 C atoms, where the substituents are selected from the group consisting of OH, OCH.sub.3, COOM and SO.sub.3 M; aralkyl; aryl or substituted aryl, where the substituents are selected from the group consisting of OCH.sub.3, Cl, Br, COOM and SO.sub.3 M; or where R.sub.3 and R.sub.4 together form a ring with or without a hetero atom; PA1 R.sub.2 represents alkyl with 1 to 6 C atoms; PA1 and PA1 M represents hydrogen, a metal cation or an ammonium cation, which may be substituted by one or more alkyl or substituted alkyl groups each having from 1 to 12 C atoms. PA1 (i) a compound of general formula (5) ##STR6## PA1 wherein R.sub.2 is as described above, is reacted with a compound of formula (6) ##STR7## PA1 wherein n, R.sub.1 and M are as defined above, under conditions that one of the chlorine atoms of the dichlorotriazine of formula (5) is replaced by the compound of formula (6); PA1 and PA1 (ii) the disubstituted triazine is reacted with a compound of general formula (7) ##STR8## PA1 wherein R.sub.3 and R.sub.4 are as defined above, under conditions that the third chlorine atom of the triazine ring is replaced by the compound of formula (7).